It is well known that cutting speeds can be maximized by employing teeth which have a large relief angle. The disadvantage of using large relief angles however is that the resultant stress on each tooth is so great that chipping occurs with considerable frequency and hence the life of the blade may be quite short, depending of course on other factors such as the type and hardness of material being cut, and also speed, depth and pressure of cut. The high rate of chipping is believed to be traceable to the fact that a saw tooth which has a large relief angle has a comparatively small tooth angle so that the tips of the teeth become weak. A short blade life results not only in frequent replacement of the blade but also substantial downtime, or non-cutting time, to allow for blade replacement. In making an economic assessment of the cost of performing a given job, all of these factors--blade cost, downtime, etc. must be taken into consideration.
It is also known that the frequency of chipping can be reduced and thus the life of the blade increased, and blade change downtime reduced, if a blade is used in which the relief angle of the individual teeth is small. The decreased rate of chipping in such a saw tooth is believed attributable to the presence of a larger tooth angle which increases the strength of the teeth tips. The disadvantage of using a small relief angle however is that the cutting resistance is increased with the result that the speed of cut is much slower, as contrasted to the speed of cut with teeth having large relief angles, for the same job. Again, in making an economic assessment of the cost of performing a given job with teeth having small relief angles, all relevant factors--blade cost, downtime for blade changeover, etc., must be taken into consideration and it is possible that even though blade consumption can be decreased as contrasted to teeth having large relief angles, the additional cutting time offsets these advantages.
It should also be noted that in many shops improper cutting procedures are often employed despite the strenuous educational efforts by management and saw blade manufacturers which attempt to educate blade users on the shop floor to match the blade, together with other factors such as feed rate and pressure, to the job. Thus, for example, hard material should generally be cut at a slower lineal blade speed than softer material. However, resetting of a saw's operating functions each time a sawing job is required is a time-consuming task which requires a skill level and attention to detail which is lacking in many shops. This is particularly true in small shops which have short runs on different materials as contrasted to high-production shops which may have sufficiently long runs on the same material to justify the extra effort and care required to match the saw conditions to the job on a job-by-job basis. Thus, in many small shops the same sawing parameters are used from job to job, including blade, speed, pressure, etc. As a consequence, over a period of time sawing operations are not performed as cost effectively as they could be if the sawing parameters more closely matched the sawing requirements.
There is thus a need for a general-purpose saw blade which will saw different materials cost effectively; that is, a single saw blade which combines, or substantially combines, the fast cutting speeds inherent in saw teeth having large relief angles and small tooth angles, with the resistance to chipping which characterizes saw teeth having a small relief angle and a large tooth angle.